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(N0 Model-J M. G. KELLOGG. MULTIPLE SWITGHBOARD.

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HIIM 6 Patented Oct. 26,1897

Q 0 ri Nrrnn STATES PATENT FFICE.

MILO G. KELLOGG, OF CHIOAGO, ILLINOIS, ASSIGNOR TO THE KELLOGG SlVlTC-HBOARD AND SUPPLY COMPANY, OF SAME PLACE.

MULTIPLE SWITCHBOARD.

SPEBIFICATION forming part of Letters Patent No. 592,389, dated October 26, 1897.

Application filed September 4, 1890. Serial No- 363,961. (No model.)

To alt whom it may concern.-

Be it known that I, MILO G. KELLOGG, of Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Multiple Switchboards for lelephone-Exchanges, of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to a telephone-exchange system in which the lines are singlecircuit lines grounded at their outer ends and normally grounded at the central office; and it consists in a system of testing the lines to determine whether they are in use.

In the drawings illustrating my invention, Figures 1 and 1 represent sections of two multiple switchboards of the exchange to which the same lines are connected. Fig. 2 shows a diagram of the boards with the mainline apparatus and connections necessary to illustrate my invention. Fig. 3 shows a diagram of an operators cord system to be used in connection with the boards. Fig. 4: shows an operators test system to be used at the board. Fig. 5 shows a subscribers'station apparatus.

In Fig. 2, A is a sectional view of the switchboard shown in Fig. 1, and A is a sectional View of the switchboard shown in Fig. 1", each as indicated bythe line 01 e.

I place as many boards in the central office as are found necessary or desirable in order to properly operate the exchange. On each board isa spring-jack or othersuitable switch for each line. Each switch has a contactspring which normally connects with an insulated contact-piece and is adapted to receive a loop-plug and, when a plug is inserted, to disconnect the spring from the contact-piece and connect the two contact-pieces of the plug with the spring and said insulated contact-piece, respectively. The switch is also adapted to receive a single-contact switch-plug and, when a plug is inserted, to disconnect the spring from the contactpiece and connect the spring with the contact piece of the plug. In the construction of the switches as shown and as will hereinafter be described I prefer to have a contact-point electrically connected with the contact-piece and on which the spring normally bears, as there is less chance of poor connection when the spring bears on a point than when it bears on a surface adapt-ed to be brought into connection with the plug-contacts.

In Fig. 2, g 9 represent the springs of the different switches, h 72. the contact-points on which the springs normally bear, and jj the contact-pieces of the switches connected with the points h h. l Zare the switch-holes. CL 1) are the rubber strips on which the metal parts of the switches are mounted, as shown, and through the fronts of which are the switch-holes Z Z. The contact-pieces j j are so placed along one of the surfaces of the plugholes as readily to form connection with one of the contact-pieces of the loop-plugs. The holes Z Z are adapted to receive the switchplugs shown in Fig. 3 and marked D D, and when a plug is inserted into a switch it raises the spring g from the contact-point h, and the spring g and the contact-piece of the plug are in contact. I These holes are also adapted to receive theloop plug shown in Fig. 4, and when a plug is inserted into a hole it raises the spring of the switch from the contact-point h, and the spring g and the contact-piece j of the switch arein contact with the two contact-pieces of the plug, respectively.

w and a: are calling-annunciators, one for each of the lines shown.

Each annunciator has a pair of contactpoints normally (or when the annunciator does not indicate a call) in contact with each other, but which are separated by the annunciator while it indicates a call. The two contact-points of a pair are marked p and q, respectively. One of them, q, is a spring-contact which is pressed by the annunciatordrop, when the drop falls, away from its cor responding contact-point p. The contactpoint p is represented as an angle piece which passes over the spring q and is in contact with the spring when the spring is not actuated by the annunciator-drop. y

Two lines are shown in the drawings, one marked line No. 1 and the other line No. 2. These lines are ordinary single-circuit lines grounded at their outer ends and having at the subscribers stations any usual and approriate subscribers-station a aratus... Each P line passessuccessively through the pairs of contacts of its switches on the several boards, passing in each case to the spring first. It then passes through its line-annunciator and the pair of contact-points of the annunciator to the common ground wire or connection of the lines. The circuit of each line. shown may thus be traced in Fig. 2.

In the operators cord system shown in Fig. 3, D D are the switch-plugs of a pair of cords. n n are the rubber insulations of the plugs, andm mare their contact-pieces. Thesecontact-pieces pass each to the bottom of its plug and are adapted to rest normally, or when the plug is not in use, on the metal piece 0, which then connects it with the ground. Weights, as is usual, or similar devices may be used to bring the contact-pieces of the plugs into contact with the piece and secure a good connection. These plugs are adapted to be inserted into any of the switches at their board,

' and when a plug is inserted it operates the switch, as above described. The plugs should.

be inserted so that the contact-piece m is in contact with the spring g. The connections of the lines might be reversed, so that the. lines pass first-to the contact-piece j of each of their switches, and in that case the plugs should be inserted in such a position that their contactpieces form connection with the pieces j of the switches. Y is the looping-in switch forthe pair of cords. shown.

K is the calling-key, and 'L" is a clearing-out annunciator. t is the operators telephone,

The operation of the system in connection with the switchboards will be apparent to those skilled in the art.

litfwill readilybe apparent that when a line is. switched by the insertion of a plug intoi'ts switch the line is disconnected from its normal ground-wire at the central OfflCG: and is connected into a circuit with the pair of cords. Only one pair of cords is shown, but the connection of such other pairs, with their accompanying apparatus, as the operator may need will be apparent to those skilled in the art.

a looping-in switch, a clearing-outannunciator, and a. calling-key. One telephone and one calling-generator will answer for her'system of cords.

In' the operatorsv test system shown in Fig. 4, T is a loop test-plug adapted tobezinserted intoany of the switches and when inserted tooperate them, as heretofore described.

a test-battery, and Sisa test receiving instrument. The instrument and battery are; connected in a loop-which terminates in the. two

B is

calling-generator. 3 is. the signal-receiving bell. 4 is the subscribers telephone. 5 is the secondary, and 6 is the primary, of the induction-coil. 7 is the transmitter. 8 is the transmitter-battery. 9 is a condenser. These parts may be of usual forms of apparatus and are connected as shown or in other ways so as to perform practically the operations required and the operations hereinafter described.

When the subscribers telephone is on its ary of the induction-coil, and the condenser are shunted by a wire of small resistance, so as to be practically out of the circuit. the telephone is off the switch, the telephone,

the secondary of the induction-coil, and the condenser are in the circuit and the signalbell is practically out of the circuit.

The test receivin g instruments and test-batteriesshould be so constructed and adjusted to each other and the circuits that the inst-rument will sound or respond when it-and the j battery are looped into the closed circuit of any single line and the subscribers telephone is not off its switch for use, but will not respond if the circuit is open at any point or if the su-bscribers telephone is cit its switch and the; condenser at the subscribers station is included in the circuit, or the line is switched with another line and thereby has its test-circuit open, as will hereinafter be in- :dicated, or the resistance of two lines is in f the circuit in which the instrument and battery are included.

and B is her calling generator or battery. The circuits are substantially as shown.

The operation of the test system is as folwith the contact-pieces of the plug. If, then,

the line is not switched at any board and the annunciator does not indicate a call and the subscribers telephone is on its switch, the test receiving instrument will sound or respond, indicating that the line is free tobe switched to. switched, the subscriber has sent in a call and the annunciator indicates the call, or To each pair of cords, with its pings, belong If, however, the line notbeing has taken his telephone from, the switch for i switch, the signal-receiving bell is in the cir- 1 cuit of the line, and the telephone, the second- IIO use, the instrument will not sound, as the If, again, the line is switched 1f, again, the

iline is switched atany board with another 1 line and the test. is made in some switch between' the one used for switching and the subscribers station, the instrument will not sound on account of the resistance of two lines being in the circuit in which the test receiving instrument and battery are included.

WVhen a test of a line is made and the test receiving instrument sounds, the operator knows that neither the line nor the operators telephone is switched for use nor the line-annunciator indicates a call, and when the instrument does not sound she knows that either the annunciator indicates a call or the subscribers telephone is switched for use or the line is switched for use, and she will not connect the line with any other line. By this system a subscribers line is reserved to himself from the time he sends in his call or takes the telephone down for use.

In multiple-switchboard systems an operator to whom certain lines are assigned to answer frequently receives several calls at practically the same moment, and it may require some time before she can switch to a certain line and answer its calls.

In systems in which the test depends only on the line being switched at some board another operator may in the meantime test the line and finding it to test free may switch it with another line and cause annoyance and confusionto the subscriber. This cannot occur in this system of testing, because as soon as the subscriber takes his telephone from its switch the line will test busy whether or not it is switched at the central oifice. Again, in systems of testing which depend only on the subscribers telephone being on or off its switch confusion frequently arises from the fact that a subscriber places his telephone on its switch .when he-is through conversation without sending in a clearing-out signal, and his line tests free and is connected to when it is already switched with another line. Lines in this condition are technically called tied npt This, again, cannot occur in this system, because the line will test busy until it is disconnected at the central office whether or not the subscribers telephone is on its switch. The system therefore combines the advantages and obviates the disadvantages of the two general systems of testing outlined above. Moreover, in this system the line tests busy as soon as the callinggenerator operates, and the annunciator indicates a call whether the subscriber may have taken down his telephone for use or have replaced it on its switch.

I claim as myinyent-ion and desire to secure by Letters Patent- 1. In a telephone-exchange system, a telephone-line normally on closed circuit, in combination with a subscribers-station apparatus having a telephone, a telephone-switch, a condenser, contacts and connections by which the condenser is switched in the line-circuit while the telephone is switched for use but not otherwise, a test-loop containing a test receiving instrument and battery and switch apparatus by which such loop may be connected in the normally closed circuit, the instrument being so constructed and adjusted to the circuits and battery that it soundsor responds when included in the normal linecircuit but does not respond when on open circuit or in circuit with a condenser or in a circuit which has also the resistance of a second line, substantially as set forth.

2. In a telephone-exchange system, a tele phone-line normally on closed circuit, in combination with a subscribefis-station apparatus having a telephone, a telephone-switch, a condenser, contacts and connections by which the condenser is switched into the line-circuit while the telephone is switched for use but not otherwise, switching apparatus by which the line may be switched with another line, a test receiving instrument, switching apparatus whereby the instrument may be included in the normal circuit of the line, and a battery in the circuit thereby established, the instrument being so constructed and so adjusted to the battery and the circuit that it sounds or responds when connected into the normal circuit but does not respond when on open circuit or in circuit with a condenser or in a circuit which has also the resistance of a second line, substantially as set forth.

3. In a telephone-exchange system, telephone-lines grounded at their outer ends and multiple switchboards for the lines, each board containing a switch for each line, each switch having a pair of contact-points normally in contact, adapted to receive a switchplug and when the plug is inserted to have the contact-points separated and the contact piece of the plug in contact with the line contact-point of the switch and with that only, and adapted to receive a loop test-plug and when the plug is inserted to have the contactpoints separated and connection made betweenthem and the two contact-pieces of the plug, respectively, each line passing successively through the pairs of contact-points of .its switches on the boards, passing in each case to the line-point first and from the last switch to the ground, in combination with a subscribers-station apparatus for each line, containing a telephone, a telephone-switch, a condenser, contacts and connections by which the condenser is included in the'circuit of the line when the telephone is switched for use but not otherwise, a loop test-plug and a test receiving instrument and battery at each board, said instrument and battery being included in a loop the two ends of which terminate in the two contact-pieces of the plug, the instrument being so constructed and so adjusted to the battery and the circuits that it will sound or respond when the plug is inserted into the switch of any line in its nor mal condition but will not respond when on open circuit or in circuit with a condenser or in a circuit which has also the resistance of a second line, substantially as set forth.

4. In a telephone-exchange system, a telephone-line normally 011 closed circuit, and an ann unciator normally in circuit with the line with a pair of contact-points in its circuit normally closed but open while the annunciator indicates a call, in combination with a subscribers-station apparatus having a telephone, a telephone-switch, a condenser, contacts and connections by which the condenser is switched in. the line-circuit while the telephone is switched for use but not otherwise, a test-loop containing a test receiving instrument and battery,- and switch apparatus by which such loop maybe connected in the nor-. mally closed circuit, the instrument being so constructed and adjusted to the circuit and battery that it sounds or responds when included in the normal line-circuit but does not respond when on open circuit or in. circuit with a condenser or in a circuit which has also the resistance of a second line, substantially as set forth.

5. In a telephone-exchange system, a telephone-line normally on closed circuit, and an annunciator normally incircuit with the line with a pair of contact-points in its circuit normally closed but open while the annunciator indicates acall, in combination with a subscrib'ersstation apparatus having a telephone, a telephone-switch, a condenser, contacts and connections by which thecondenser is switched into the line-circuitwhile the telephone isswitched for usebut not otherwise,

' switching apparatus by which the line may be switched with another line, a test receivin g instrument, switching apparatus whereby the instrument may be'included in the normal circuit of the line, and. a battery in its circuit thereby established, the instrument being so constructed and so adjusted to the battery and the circuit that it sounds or responds when connected into the normal circuit but does not respond when on open circuit or incircuit with acondenser or in a circuit which I has also the resistance of a second line, substantially asset forth.

6. In a telephone-exchange system, telephone-lines grounded at their outer ends and multiple switchboards for the lines each board containing a switch for each line, each switch having a pair of contact-points normally in contact, adapted to receive a switch-plug and I when the plug is inserted to have the contactpoints separated and the contact-piece of the plug in contact with the line contact-point of the switch and with that only, and adapted I to receive a loop test-plug and when'the plug is inserted to have the contact-points separated and connection made between them and the two contact-pieces of the plug, respectively, each line passing successively through the pairs of contact-points of its switches on the boards, passing in each case to the linepoint first and from the last switch to the ground, and an annunciator normallyin circuit with the line with a pair of contact-points in its circuit normally closed but open while the annunciator indicates a call, in combination with a subscribers-station apparatus for each line, containing a telephone, atelephone switch, a condenser, contacts and connections by which the-condenser is included in the circuit of the line when the telephone is switched for use but not otherwise, a loop test-plug and a test receiving instrument and battery at each board, said instrument and battery being includedin a loop thetwo ends of which terminate in the two contact-pieces of the plug, the instrument being so constructed and so adj usted to the battery and the circuits that it will sound or respond when the plug is inserted into the switch of any line in its normal condition but will not respond when on open circuit or in circuit with a condenser or in a circuit which has also the resistance of a second line, substantially as set forth.

In witness whereof I hereunto subscribe my name this 23d day of June, 1890.

' MILO G. KELLOGG. Witnesses:

- EMIL ABENHEIM,

(J. STRICH-CHAPELL. 

